The general field of technology of the present invention is in signal processing of multiplexed far infrared (IR) imaging systems.
One approach to far infrared imaging systems is to use a linear array of detectors coupled through buffer amplifiers to a time division multiplexer to produce a serial output corresponding to scanning the detectors along the array. A combination of optical scan in one direction and electronic scan in the other produces raster scene scan. A cathode ray tube readout may then be coupled and synchronized to produce a visible raster picture.
Recently, time division multiplexers have been constructed using charge coupled devices (CCDs). These devices can operate at low temperatures making multiplexing inside the detector dewar possible. However, the response of an array of detectors to a given input signal varies from detector to detector. This response variance requires that the gain associated with each channel be changed to normalize the outputs prior to multiplexing. This is usually done in the buffer amplifiers. In systems where the multiplexer must operate with fixed gain inputs such as a monolithic CCD device in the dewar, it is not possible to set each gain individually nor to perform automatic responsivity equalization. To make multiplexing in the dewar practical some means of equalizing the serial output must be used. The present invention accomplishes equalization of the serial output.